This invention relates to a dyna-bender, and more particularly to one which has a minimum number of parts.
To exercise arms and wrists, various dyna-benders have been developed. For example, U.S. Pat. No. 4,489,937 disclosed a safety dyna-bender as shown in FIG. 1. The safety dyna-bender has two handle pipes 11 and 12 for connecting two hollow grips 13 and 14 to two ends of a coil spring 10. In this safety dyna-bender, a center cord (not shown) interconnects the inner walls of the hollow grips 13 and 14 for effectively protecting the user against any unexpected accidents resulting from the breaking of the coil spring 10 during exercise. To mount the center cord on the grips 13 and 14, cupshaped positioning anchors (not shown) are provided in the grips 13 and 14. These anchors complicate the dyna-bender thereby increasing its manufacturing cost. Also, the handle pipes 11 and 12, which are provided to interconnect the coil spring 10 and the grips 13 and 14, further increase its manufacturing cost. The coil spring 10 has two distal ends A and B which are undesirably exposed to the exterior of the handle pipes 11 and 12. In addition t their unsightly outer appearance, the exposed ends A and B of the coil spring 10 sometimes injure the user. When the total length of the dyna-bender is fixed, if the handle pipes are provided, the length of the coil spring will be shortened, reducing the exercise effect.
U.S. Pat. No. 2,714,008 disclosed a dyna-bender shown in FIG. 2. It includes an external coil spring 15 and an internal coil spring 16 extending through the external coil spring 15. Although the internal coil spring 16 increases the exercise effect for the user, additional elements are needed to secure the ends of the internal coil spring 16 to the grips. In addition, the exposed ends of the coil spring and the handle pipes are still present.